1. Field of the Invention
This invention relates to X-ray filters, for example for use in X-ray examination apparatus, and in which the filter comprises an array of filter elements each comprising a vessel containing an X-ray absorbing liquid.
An X-ray filter of this type is described in WO 97/03450.
2. Description of Related Art
One particular problem which arises in the manufacture of an X-ray filter of this type is the feeding of signals to the filter elements. The filter setting is adjusted by changing the level of liquid for the individual filter elements, and for this purpose an individual control line is required for each filter element.
As the filter elements comprise a vessel, for example a capillary, they cannot be defined as semiconductor circuit components on a substrate. However, the control circuitry, which is arranged to provide signals to the control lines, is most conveniently arranged as an array of semiconductor switching devices on a common substrate, for example an array of thin film transistors. The problem therefore arises in forming electrical connections from the control circuit to the array of filter elements.
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant""s invention of the invention subsequently claimed.
According to a first aspect of the present invention, there is provided an X-ray filter comprising an array of filter elements and a control circuit, the control circuit comprising an array of switching devices provided on a common substrate, a switching device being provided for each filter element for switching a control signal to the respective filter element, an output terminal of each switching device being provided with an external connection portion located at the respective switching device, an array of external connection portions thereby being provided over the array of switching devices, and wherein the connection portions are bonded to a connection block of the array of filter elements.
The use of a connecting portion arranged at each switching device avoids the need to use edge connections from the control circuit. This may not be possible, since these edge connections may already be used for supplying control signals to the array of switching devices. For example, the switching devices may comprise thin film switching elements on a common substrate and which are supplied with control signals from integrated circuit driver chips. The edges of the control circuit substrate, for example a glass substrate carrying an array of thin film transistors, may already be used for connections to the driver chips.
The external connection portions may comprise metallic bumps formed by stud bumping, and the metal is preferably gold.
The connection block of the array of filter elements may comprise a plurality of connected parallel membranes each carrying a plurality of conductors, each conductor leading along its respective membrane to an associated filter element. Bonding of the external connection portions to the array of filter elements then connects each external connection portion with the end of an associated conductor.
Glass spacers may be provided between the membranes, which assists in matching the temperature coefficient of expansion of the connection block with that of the control circuit, which may include a glass substrate.
The filter element array and the array of switching devices are preferably arranged in rows and columns with each membrane carrying the control signals for an individual row or column of the array of filter elements. Arranging the filter elements and switching devices in corresponding arrays simplifies the connection between the two arrays. The array of switching devices may have the same pitch as the array of filter elements, to simplify further the interface of the control lines to the array of filter elements.
Each filter element preferably comprises a capillary containing an X-ray absorbing liquid, the X-ray absorptance of each filter element being adjustable by controlling the level of the liquid in the capillary using the control signal. The membranes of the connection block may then form the capillaries or else they may be interleaved with further membranes which form the capillaries, the further membranes then being provided with conducting tracks which lead to the individual capillaries.
According to a second aspect of the present invention, there is provided an X-ray examination apparatus comprising an X-ray source, an X-ray detector and a filter of the first aspect of the invention.